The present invention is directed to a whitewater dispersant formulation suitable for dispersing fibers in a slurry for deposition in a wet-laid mat process. More particularly, the present invention is directed to a whitewater formulation which contains a cationic polyacrylamide and is suitable for manufacturing a wet-laid mat of glass fibers.
Fiber glass mats are used as reinforcing elements for roofing shingles, flooring, wall coverings, and the like. One technique of manufacturing these mats is to disperse amounts of chopped-strand glass fibers in an aqueous slurry, collect the fibers on a foraminous belt using suction to dewater the slurry, apply a binder to the mat to provide the desired strength properties to the mat, and heat the binder-containing mat in an oven to drive off excess moisture and to cure the binder.
Certain properties of the mat, including tensile strength and, in some cases, the suitability of the mat for a particular application, will depend, in good measure, on how well the fibers are dispersed within the slurry. This ultimately determines the distribution of fibers in the mat, the quantity of holes or clumps in the mat, etc. The whitewater dispersant system plays the major role in achieving the desired fiber dispersion and distribution.
There are a number of traits desired in a whitewater dispersant system and these traits can be provided by the various components. Typically, a whitewater will include some level of surfactant to be deposited on the fibers to make them slip relative to one another. While certain amounts of surface treatments can be applied in the form of sizings as the fibers are made, additional surfactants are generally necessary to achieve proper dispersion of the fibers in the slurry. However, it is important that an excessive amount of surfactant not be applied to the fibers or their surfaces will be too slippery to be bonded together.
Another desired property of a whitewater dispersant system is a sufficiently high viscosity (e.g., from 2 to 12 cps, preferably around 8 cps.) to hold the fibers in suspension. To produce such a viscosity a "thickener" or viscosity modifier must be added. Any such viscosity modifier should be compatible with the other whitewater components. The surfaces of most glass fibers are generally slightly anionic. Accordingly, it is preferred that the surface treatments (sizings and surfactants) be cationic to form a better bond with the glass surfaces. Hence, it is important that the viscosity modifier be either nonionic or cationic so as not to react with and precipitate out the surfactant and not to react with the cationic sizing on the fibers causing them to flocculate.
A third desired property of whitewater need be stated in terms of what is not desired. If the ingredients create a large amount of foam (i.e., if the whitewater has a great deal of entrained air) particularly of the microbubble size, the foam tends to cause pumping difficulties including possible cavitation in, or other failure of, the moving parts of the pump. The microbubbles are particularly stable (i.e., difficult to deaerate). Typically, a defoamer will be used to try to decrease the level of air entrained in the whitewater.
The whitewater dispersant system of the present invention comprises a cationic surfactant and a cationic viscosity modifier in water. Various amounts of an additional viscosity modifier in the form of a nonionic hydroxyethyl cellulose may be added, preferably, from 50 to 75% of the total viscosity modifier present in the whitewater. As noted above, the cationic surfactant is preferred for its superior bonding to the anionic glass surface. The cationic viscosity modifier is wholly compatible with both the surfactant and the sized fibers. In addition, it was found that between 25 and 50% of the cationic polyacrylamide, when used in conjunction with 75 to 50% hydroxyethyl cellulose, significantly reduced the amount of air entrained into the whitewater and, hence, reduced pumping difficulties caused by such entrained air when circulating the large quantities of whitewater needed for wet process mat formation.
Various other features, characteristics and advantages of the present invention will become apparent after a reading of the following description.